The present invention relates to a new and improved control apparatus having a switch assembly which effects a control function upon actuation of a valve.
A known power steering apparatus includes a control assembly which is connected with an engine driven pump and with a motor which is connected to steerable vehicle wheels. The control assembly includes a gerotor gear set having internally and externally toothed gears. The gerotor gears are rotatable and orbital to meter fluid flow from the pump to the motor. A directional control valve is moved in response to actuation of the gerotor gear set upon initiation of a steering operation. When the vehicle wheels have been turned to an extent corresponding to the extent of rotation of the input shaft, a biasing spring returns the directional control valve to its neutral or initial position. Steering control assemblies which operate in this manner are disclosed in U.S. Pat. No. 3,895,888 and in German Offenlegungsschrift No. 1,553,287.
Power steering devices have been used in electric vehicles, such as fork lift trucks. In these vehicles, a power steering fluid supply pump may be driven by an electric motor. The motor continuously drives the pump even though the wheels of the vehicle are not being turned and there is no demand for steering fluid. Continuous operation of the motor to drive the power steering pump is objectionable because it constitutes an unnecessry drain on the vehicle battery.
In an effort to reduce the drain on the battery of an electric vehicle, it was suggested in U.S. Pat. No. 3,991,846 that a motor which drives the power steering pump be energized only during steering operations. In this patent, rotation of a steering wheel effects manual operation of a metering pump. Manual operation of the metering pump is effective to generate a fluid pressure which is directed to a control valve. This pressure actuates the control valve to direct fluid pressure from the manually actuated metering pump to a piston type actuator which changes the force exerted against a carbon pile type switch. Changing the force exerted against the carbon pile changes the resistance in an electrical circuit which energizes a motor to drive the power steering fluid supply pump.